Merge "init README: document AIDL service interface"

  Currently defaults to root.  (??? probably should default to nobody)

`interface <interface name> <instance name>`

> Associates this service with a list of the HIDL services that it provides. The interface name

  must be a fully-qualified name and not a value name. For instance, this is used to allow

  hwservicemanager to lazily start services. When multiple interfaces are served, this tag should

  be used multiple times.

  For example: interface vendor.foo.bar@1.0::IBaz default

> Associates this service with a list of the AIDL or HIDL services that it provides. The interface

  name must be a fully-qualified name and not a value name. For instance, this is used to allow

  servicemanager or hwservicemanager to lazily start services. When multiple interfaces are served,

  this tag should be used multiple times. An example of an entry for a HIDL

  interface is `interface vendor.foo.bar@1.0::IBaz default`. For an AIDL interface, use

  `interface aidl <instance name>`. The instance name for an AIDL interface is

  whatever is registered with servicemanager, and these can be listed with `adb

  shell dumpsys -l`.

`ioprio <class> <priority>`

> Sets the IO priority and IO priority class for this service via the SYS_ioprio_set syscall.